The present application is based on Japanese patent application 2000-300017 filed on Sep. 29, 2000, which is hereby incorporated herein by reference, in its entirety.
1. Field of the Invention
The present invention relates to a thermoelectric module which may be an optical communication semiconductor laser diode module, a semiconductor amplifier module, an external electro-absorption modulator, a reception module, etc.
2. Discussion of the Background
The environmental setting of a thermoelectric semiconductor laser diode module, in other words the external ambiance of the laser diode module, can approach a temperature of 60xc2x0 to 70xc2x0 C. due to the generation ofjoule heat in the various electric parts. In a laser diode used as a light source in high speed optical fiber communication, when the ambient temperature changes, the optical characteristics also change, so that the wavelength of the laser diode changes. Therefore, a tip-carrier equipped with a laser diode is isolated thematically from the module case. In order to thermally isolate the laser diode and keep its temperature constant, a thermoelectric module having a controlled temperature is used in general.
The thermoelectric module with controlled temperature is made by joining the insulating body enclosing the electrodes and the semiconductor tips. When heating or cooling by using the thermoelectric module, the construction is joined to another member via further soldering material, such as shown in Japanese laid open publication patent tokkai-hei 10-62659.
For example, in the case of using the thermoelectric module for cooling, the soldering material used for joining the thermoelectric module to the physical object to be cooled or the construction body for exoergio (a heat sink or a box case etc.), has a lower melting point temperature (solidus, liquidus) than the soldering material joined the tips between the two insulations. The reason is to prevent deformation and destruction of the thermoelectric module when joining. Selection of soldering material is decided while making an allowance of a safety ratio in regard to the generation of over-shoot of the temperature of the heat process.
Furthermore, in the case where high heat resistance is required, as disclosed in pages 24 to 25 of xe2x80x9cThermoelectric Transfer System Technical General Handbookxe2x80x9d published by Realize Company, published Jun. 30, 1995, in general 95Sn5Sb solder is used because when the semiconductor tips are joined the heat resistance of the semiconductor adds to the heat resistance of soldering material.
However, as above-mentioned, the joining of the encasing body and the construction for heat release uses a soldering material having a lower melting point temperature (solidus, liquidus) than the soldering material joining the semiconductor tips. Therefore, when high heat resistance is required, there is the problem that the heat resistance and the reliability of the joint of the insulating body and the construction for heat release deteriorates.
Furthermore, in regard to using 95Sn5Sb solder for joining tips, when we select soldering material for joining the insulating body for exoergic side (heat release side) to the semiconductor tips and we select solder material having a high heat resistance with a lower melting point than 95Sn5Sb solder, there is the problem that most soldering material includes Pb having an adverse environmental effect.
It is an object of the present invention to solve the above-mentioned disadvantages.
According to one feature of the present invention, a thermoelectric module comprises a case, P-type and N-type semiconductor tips having an exoergic side and an endoergic side, said P-type and N-type semiconductor tips being positioned in said case, an insulating base plate for the exoergic side positioned in said case, an insulating base plate for the endoergic side positioned in said case, a first soldering layer which joins the insulating base plate for the exoergic side to said case via first soldering material, and second soldering layers which respectively join the P-type and N-type semiconductor tips to the insulating base plate for the exoergic side and the insulating base plate for the endoergic side using a second soldering material, wherein a melting point temperature of first soldering material for the first soldering layer is higher than a melting point temperature of the second material for the second soldering layers.
Therefore, the thermoelectric module according to the present invention can have high heat resistance for the soldering material at the exoergic side, even though solder such as 95Sn5Sb solder is used.
According to another feature of the present invention, a process for producing a thermoelectric module including P-type and N-type semiconductor tips having an exoergic side and an endoergic side, comprises a first step of joining a case to an insulating base plate via a first soldering layer of a first soldering material, a second step of joining an insulating base plate for the endoergic side to the P-type and N-type semiconductor tips via a second soldering layer of a second soldering material, and third step of joining an insulating base plate for the exoergic side to the P-type and N-type semiconductor tips via a second soldering layer of the second soldering material, wherein a melting point temperature of first soldering material for the first soldering layer is higher than the melting point temperature of second material for the second soldering layers.
Therefore, the thermoelectric module can be prevented from deformation and destruction.
Furthermore, according to the present invention, the semiconductor tips do not produce heat when joining the insulating base plate for the exoergic side, so that we can use soldering material which needs heat more than 300xc2x0 C., that could not be used heretofore in relation with heat resistance of the tips at soldering. Furthermore, we need not use solder material comprising Pb.